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Low Profile Bridge Rail

Question
State IA
Description Text

Kimball Olson from the Office of Bridges & Structures at IaDOT, gave me your name.  We are considering using the Low-Profile Bridge Rail (see attached PDF) on the 9th St. bridge in downtown Des Moines (over I-235).  This would act as a pedestrian/traffic barrier.  However, there are intersections right at the end of the bridge.  This is preventing us from using the 108" End Section.  I was wondering if this end section could be shortened to 2.1m (83") and still meet TL-2 requirements for 30 mph.  I've also attached a PDF of the details we have on this barrier.  Do you have any other detail sheets?  It seems we're missing a few details.

Keywords
  • Bridge Rails
Other Keywords none
Date April 9, 2007


Response
Response

The low-profile bridge rail was developed by MwRSF/UNL several years ago as part of the Pooled Fund Program. Details of this barrier system are contained in the report. Although it may seem that there are few details, it was not that complicated of a system. However, I will check to see whether we have any other details.

In your email, you mentioned that you desire to change the end slope and section length from 108 in. to 83 in. Actually, the report details show the end section length to be 180 in. As such, your proposed change is fairly drastic in terms of changing the end slope. In addition, our developed effort focused on the interior design and structural capacity. The geometry of the end section was adopted from the TTI low-profile barrier since they crash tested their end section. We did not crash test our end section but use their geometry to avoid the need to do so. If the end section is changed, I believe that you would be required to crash test the new proposed end section according to the NCHRP 350 requirements.

Second, I believe the adaptation of the low-profile bridge rail into urban situations still required research to address its use. I think Iowa submitted a problem statement last year that was written into a research proposal (attached) but unfunded in the Year 17 program. Originally, the low-profile bridge rail was developed for situation where farm implement equipment could pass over rural bridges. For urban applications, many issues come up, including how to deal with pedestrians, how long of end treatment or bridge rail is needed to shield the hazard, are there sidewalks near the end, etc. These issues were raised in another Pooled Fund report using our best engineering judgment and standard practices. I have a feeling that this material has not yet been widely reviewed nor implemented. However, I highly recommend that you review this report (TRP-03-127-03) when attempting to implement this bridge rail in the situation noted in your email. It certainly will show you what research remains needed in the future.

P.S. " I will look for additional CAD details in the near future. Also, Iowa DOT implemented this system several years ago on a curved on-ramp or off-ramp. I believe Will Stein (formerly at IA DOT) was the individual who used it. See attached files.

Date April 10, 2007


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